Carburetor fast idle cam mechanism

Abstract

An automotive type carburetor has a fast idle cam mechanism that provides a dual path of operation that includes one ramp for engagement with the throttle valve stop screw for progressively closing the throttle valve as a function of temperature increases towards the normal operating level, and a second ramp engagable by the stop screw for automatically indexing the stop screw for an automatic return of the fast idle cam to a high cam step position upon a restart of a cold engine without necessitating any action on the part of the vehicle driver other than to render operable the vehicle ignition system.

I claim: 
     
       1. A fast idle cam mechanism for a carburetor having an air/fuel induction passage and a throttle valve rotatably mounted for a pivotal movement across the passage between an essentially closed position to a number of open positions to control the quantity of air/fuel mixture flow through the passage, a stop means fixed for rotation with the throttle valve and adapted to be stopped at times in its pivotal movement in a throttle valve closing direction by frictional abutment against the face edge of a fast idle cam, an axially movable fast idle cam rotatably mounted on a shaft and including a recess in the face edge defining a cam follower slot, the slot having a closed circular track-like shape defined by a pair of side walls and arcuate turn around type end portions, the slot receiving the stop means therein, the slot having a pair of ramps each varying in radial projection along its length and together being in a side-by-side relationship and blending together at their ends at the turn around end portions of the slot forcing relative movement between the slot and stop means upon rotation of the cam, rotation of the cam in one direction moving the one ramp surface relative to the stop means engaged therewith to progressively pivot the stop means to close the throttle valve until the turn around end portion of the slot is engaged by the stop means whereupon continued rotation of the cam in the one direction moves the cam axially for engagement of the stop means with the other ramp surface, subsequent rotation of the cam in the opposite direction thereafter moving the other ramp surface relative to the stop means to progressively pivot the stop means to open the throttle valve until the other turn around end portion of the slot is engaged by the stop means whereupon further rotation of the cam in the other direction effects an axial shifting of the cam to realign the stop means with the one ramp surface for subsequent restarting closing movement of the throttle valve upon subsequent rotation of the cam in the one direction.   
     
     
       2. A mechanism as in claim 1, including spring means biasing the cam axially to align the one ramp surface for engagement by the stop means, the cam being shiftable axially in the opposite direction to align the other ramp surface with the stop means by engagement of the turn around end portion of the slot by the stop means and continued rotation of the cam in a direction camming the cam axially. 
     
     
       3. A mechanism as in claim 2, the one ramp surface having a series of circumferentially spaced steps each of a different radial projection to effect the stopping of the throttle valve stop means in a different idle speed position when engaged with the steps. 
     
     
       4. A mechanism as in claim 3, the other ramp surface having a continuously variable surface for infinitely variable changes in the pivotal movement of the stop means upon engagement with the other ramp surface. 
     
     
       5. A mechanism as in claim 4, the one ramp surface intermediate the end portions projecting further radially than the other ramp surface to define a radial shoulder therebetween for maintaining the stop means aligned with the other ramp surface during rotation of the cam in the opposite direction to prevent axial shifting of the cam by the spring means. 
     
     
       6. A mechanism as in claim 5, the steps having beveled portions urging the cam axially for disengagement of the stop means with the one ramp surface and into engagement with the other ramp surface upon a change in rotation of the cam from the one direction to the opposite direction. 
     
     
       7. A mechanism as in claim 1, including temperature responsive means connected to the cam urging the cam in the one direction of rotation upon increases in temperature above a predetermined level to progressively decrease the open position of the throttle valve. 
     
     
       8. A mechanism as in claim 7, including power means operably connected to the cam and to the engine ignition system and operable upon initial starting of the engine to rotate the cam in the opposite direction to automatically align the other ramp with the stop means and return the stop means to an end turn around portion of the slot for engagement with the one ramp surface. 
     
     
       9. A fast idle cam mechanism for a carburetor having an air/fuel induction passage and a throttle valve rotatably mounted for a pivotal movement across the passage between an essentially closed position to a number of open positions to control the quantity of air/fuel mixture flow through the passage, an abutment fixed for rotation with the throttle valve and adapted to be stopped at times in its pivotal movement in a throttle valve closing direction by frictional abutment against the edge face of a fast idle cam, a fast idle cam rotatably mounted on a shaft an including a recess in the edge face defining a cam follower slot, the slot having a closed circular track-like shape defined by a pair of side walls and arcuate turn around type end portions, the slot receiving the abutment therein, the slot having a pair of radially extending contoured cam surfaces of differing radial projection alternately frictionally engagable by the abutment, one surface being contiguous to one side wall of the slot and the other surface being contiguous to the other side wall of the slot, the surfaces blending at their ends at each turn around end portion of the slot to provide a closed circular path to effect a progressive pivotal rotation of the abutment in a throttle valve closing direction on engagement of the abutment with one surface upon rotation of the cam in one direction towards one turn around end portion of the slot and a return rotation of the abutment in a throttle valve opening direction along the other surface upon a rotation of the cam in the opposite direction towards the slot other turn around end portion, continued rotational movement of an end portion relative to the abutment camming the slot axially to realign the abutment with the other cam surface.   
     
     
       10. A fast idle cam mechanism for a carburetor having an air/fuel induction passage and a throttle valve rotatably mounted for a pivotal movement across the passage between an essentially closed curb idle engine speed position to a number of hot engine open idle speed positions and beyond towards a wide open throttle position to control the quantity of air/fuel mixture flow through the passage, a throttle valve stop rotatable with the throttle valve and adapted to be stopped at times in its movement in a throttle valve closing direction by frictional abutment against the edge face of a fast idle cam, a fast idle cam having an eccentrically disposed edge face, the cam being axially slidable and rotatably mounted on a shaft and weighted to fall by gravity in a first direction towards a position permitting closure of the throttle valve to the curb idle speed position upon disengagement of the stop from the face, thermostatic means having a one-way engagement with the fast idle cam and rotatable in the opposite direction in a throttle valve opening direction in response to temperature decreases below a set level to stop the throttle valve abutment in a hot engine idle speed position, the fast idle cam including a recess in the edge face defining a contoured cam follower slot receiving the throttle valve stop therein, the recess having first and second axially contiguous, outwardly projecting eccentric ramp surfaces adapted to be alternately engaged by the throttle valve stop, the pair merging at opposite ends, the first of the pair projecting radially a different amount than the second of the pair to define a radial shoulder therebetween, the cam being movable axially between first and second positions alternately aligning the first and second ramp surfaces, respectively, with the throttle valve stop, spring means biasing the cam to the first position to locate the stop against the first surface, engagement of the stop with the end of the slot camming the cam axially to the second position upon a predetermined rotation of the cam in the first direction, the first ramp surface having a number of circumferentially spaced steps therein of changing radial extent effecting the stopping of the throttle valve stop in different idle speed open throttle positions when engaged thereagainst upon rotation of the cam in the first direction, and power means operably connected to the cam for rotating the cam in the other direction for a return movement of the stop along the second ramp surface to merge at the end of the slot with the first ramp surface for a subsequent return movement of the cam to the first position. 
     
     
       11. A mechanism as in claim 10, the stop being engagable with the radial shoulder during engagement of the stop with the second ramp surface to permit relative movement between the stop and second surface upon rotation of the cam in the other direction without an axial shifting of the cam until the end of the slot is reached. 
     
     
       12. A mechanism as in claim 11, the power means being connected to the engine ignition system for operation in response to initial startup operation of the engine.